1. Field of the Invention
This invention relates to normally tacky pressure-sensitive adhesive compositions, and, more particularly, tapes that utilize such compositions.
2. Discussion of the Art
Pressure-sensitive adhesive tape that is especially suited for sealing boxes must exhibit a relatively high value of shear strength. At the same time, it is preferred that the tape be relatively soft and be economically feasible. On the basis of economics, it would be desirable for the adhesive to be hot-melt coatable.
U.S. Pat. No. 3,954,692 discloses a mixture of (a) an unvulcanized elastomeric block copolymer having the general configuration A - B - A wherein each A is an independently selected nonelastomeric monovinyl aromatic hydrocarbon polymer block having an average molecular weight of 2,000 to 100,000, the total block A content being from about 10 to about 50% by weight of the copolymer, and B is an elastomeric conjugated diene polymer block having an average molecular weight from about 25,000 to about 1,000,000, and (b) a compatible, thermoplastic tackifying resin containing carbon-to-carbon unsaturation therein and derived from hydrocarbons having from 5 to 8 carbon atoms and at least one carbon-to-carbon double bond therein selected from aliphatic hydrocarbons and alicyclic hydrocarbons.
U.S. Pat. No. 3,239,478 discloses an adhesive comprising a block copolymer having a general configuration A - B - A wherein each A is a thermoplastic polymer block and which is relatively incompatible with the elastomeric B segment; the average molecular weight of each A being between about 5,000 and 125,000; B is a polymer block of a conjugated diene, the average molecular eight of the blocks being between about 15,000 and about 250,000; the total of blocks A being less than about 80% by weight of the block copolymer; in addition to the block copolymer a tackifying resin and a particular extender oil, said oil being substantially incompatible with homopolymers of the aforesaid thermoplastic terminal blocks and being substantially compatible with homopolymers of the aforesaid conjugated diene. Compositions of the block copolymer described above with 5 to 200 phr (preferably 25 to I25 phr) (parts per hundred of block copolymer) of extending oil and 25 to 300 phr (preferably 50 to 200 phr) of a tackifying resin were disclosed. By adjustment of the proportions of the three basic ingredients and choice of molecular weight of copolymer, melting point and type of tackifying resin, compatibility of oil and resin with the copolymer, a hot-melt adhesive can be provided.
U.S. Pat. No. 3,753,936 discloses (A - B).sub.x Y type polymers wherein A represents nonelastomeric polymer blocks, or segments, and B represents elastomeric polymer segments. Y is an atom or group of atoms derived from a polyfunctional treating agent used in the formation of the radial polymers, and x is an integer of at least 3 and can be equal to the number of functional groups of said polyfunctional treating agent. The radial block polymer thus can be characterized as having at least three polymer branches with each branch of the radial block polymer comprising terminal nonelastomeric segments. The branches of the radial block polymer contain a terminal nonelastomeric segment attached to an elastomeric polymer segment. Although the polymer can be used in an adhesive composition, it is not expected to be useful in a hot-melt formulation.
U.S. Pat. No. 3,935,338 discloses block copolymers having at least two monoalkenyl arene polymer blocks and at least one elastomeric conjugated diene polymer block. The macromolecular configuration may be either linear or radial dependent upon the method by which the block copolymer was formed. Typical block copolymers of the most simple configuration would have the structure polystyrene-polyisoprene-polystyrene, and polystyrene-polybutadiene-polystyrene. The adhesive composition of U.S. Pat. No. 3,935,338 calls for 25 to 100 parts by weight extending oil per hundred parts by weight rubber. The addition of even a moderate amount of oil drastically reduced the peel adhesion and the shear adhesion failure temperature, thus indicating that such compositions would be unsatisfactory in many adhesive applications even though the addition of oil did, in fact, substantially reduce the viscosities of the hot melts derived therefrom.